Not applicable.
Not applicable.
This invention relates to processes for the production of a gas containing hydrogen and carbon oxides (such as methanol synthesis gas) by steam reforming a hydrocarbon feedstock, and in particular to an apparatus and method for hydrocarbon reforming processes which utilize high grade sensible heat of flue gas and product synthesis gas to generate additional product gas and minimize steam export.
The steam reforming process is a well known chemical process for hydrocarbon reforming. A hydrocarbon and steam mixture (a xe2x80x9cmixed-feedxe2x80x9d) reacts in the presence of a catalyst to form hydrogen, carbon monoxide and carbon dioxide. Since the reforming reaction is strongly endothermic, heat must be supplied to the reactant mixture, such as by heating the tubes in a furnace or reformer. The amount of reforming achieved depends on the temperature of the gas leaving the catalyst; exit temperatures in the range 700-900xc2x0 C. Are typical for conventional hydrocarbon reforming.
Conventional catalyst steam reformer processes combustor fuel to provide the energy required for the reforming reaction. In a reformer of such a conventional process, fuel typically is fired co-current to incoming cold feed gas to maximize heat flux through the tube wall(s) by radiant heat transfer directly from the flame. Downstream from the burner end, both the product gas and the flue gas exit at relatively high temperatures. The energy content of these gases usually is recovered by preheating reformer feed gas or by generating steam. As a result, the process generates excess steam that must be exported to improve the overall efficiency of the steam reforming process and to make the process economically feasible in view of the fact that significant equipment has been added to generate that excess steam.
Each of the processes disclosed in U.S. Pat. No. 5,199,961 (Osaka, et al.) and U.S. Pat. No. 4,830,834 (Stall, et al) and in European Pat. No. SP 0 911 076 A1 (Stall) utilize a portion of the available sensible energy within the reformer vessel, thereby allowing the product gas and the flue gas to exit at lower temperatures than the corresponding exit temperatures for conventional steam reforming. These reforming processes receive heat from the combustible fuel by using a combination of: (1) an equalizing wall (made of tiles, refractory, or metals) to receive radiant heat directly from the flame from which heat is transferred to the reformer tube(s) by radiant heat; and (2) an arrangement of a counter-current flow of the hot flue gas with the incoming feed which transfers sensible energy to the incoming feed by convection through the tube wall. These techniques allow the temperature of the reformer tube skin to be controlled within the design limit; otherwise, the temperature will be excessive due to the high intensive radiant heat of the flame. However, these processes suffer a heat flux limitation by avoiding the direct radiant heat from the flame to the tube as commonly used in conventional reformers.
The reformer disclosed in WO 01/12310 (Loiacono) recovers the sensible heat of product gas by the use of a tube within a tube (tube-in-tube) arrangement having catalyst in the annuli of the tube-in-tube. The cold feed in the annuli flows counter current with the combustion or the flue gas from the outside and absorbs the combustion heat by both radiant and convection heat transfers through the outside tube wall. The reformed gas flow is reversed at the end of the catalyst bed and enters the inner most passage of the tube. The reformed gas then gives up heat to the counter current flow of the incoming cold feed. The convection heat transfer process from the hot product gas to the reforming reactions, however, is not effective because there is no temperature driving force at the inversion point. As a result, more heat transfer area is required to utilize the product gas sensible heat. This arrangement uses a different inner tube configuration to provide additional surface required. However, it fails to recover high temperature sensible heat from the flue gas and suffers the same heat flux limitation as the prior art reformers discussed above.
U.S. Pat. No. 4,959,079 (Grotz, et al.) utilizes counter-current flow and a studded tube to recover the sensible heat of the flue gas for reforming but fails to recover the high temperature sensible heat of the process gas. Side-fired burners are used to maximize the heat flux to the tube. However, the side-fired burner arrangement limits the furnace to one tube row, and many burners are required. Heat lost through the furnace wall is significant as capacity increases.
A pending patent application (Air Products and Chemicals, Inc.""s Docket No. 06052 USA) teaches the use of partition walls within the radiant chamber, which resolved the excess steam generating problem. However, it requires a high temperature gas transfer line from the radiant tubes to the convection tubes, and a complex tube arrangement that is difficult to scale up or down in terms of capacity.
It is desired to have an apparatus and a method for hydrocarbon reforming processes which overcome the difficulties, problems, limitations, disadvantages and deficiencies of the prior art to provide better and more advantageous results.
It is further desired to have an apparatus and a method for a hydrocarbon reforming process which utilize high grade sensible heat of flue gas and product synthesis gas to generate additional product gas and minimize steam export.
It is still further desired to have a more efficient and economic process and apparatus for hydrocarbon reforming.
The invention is an apparatus for a hydrocarbon reforming process and a method for producing a product from a steam reforming process.
The first embodiment of the apparatus includes: a combustion chamber, a convection chamber in fluid communication with the combustion chamber, at least one burner disposed in the combustion chamber, and a reaction chamber. The combustion chamber has a first end and a second end opposite the first end. The convection chamber has a first end and a second opposite the first end, the first end of the convection chamber being adjacent the second end of the combustion chamber. The at least one burner is disposed in the combustion chamber and is adapted to combustor a fuel, thereby generating a flow of a flue gas from the combustion chamber to the convection chamber, the flue gas having a sensible heat. The reaction chamber has a first part and a second part in fluid communication with the first part. A substantial portion of the first part is disposed in the combustion chamber and a substantial portion of the second part is disposed in the convection chamber. The second part is a tube-in-tube having an annular portion between an inner tubular portion and an outer tubular portion surrounding the inner tubular portion. The apparatus also includes a means for flowing a first mixed-feed through the first part of the reaction chamber, and a means for flowing a second mixed-feed through the annular portion of the second part of the reaction chamber counter-currently with the flow of the flue gas in the convection chamber.
There are several variations of the first embodiment of the apparatus. In one variation, the substantial portion of the first part of the reaction chamber is substantially vertical in the combustion chamber, and the substantial portion of the second part of the reaction chamber is substantially vertical in the convection chamber. In a second variation, the first mixed-feed flows co-currently with the flow of the flue gas in the combustion chamber. There are several variants of the second variation. In one variant, a gas having another sensible heat is injected adjacent the second end of the combustion chamber, the gas initially flowing in the combustion chamber counter-currently with the first mixed-feed. In another variant, the apparatus includes at least another burner. The another burner is located adjacent the second end of the combustion chamber, and is adapted to combustor a portion of the fuel or another fuel, thereby generating a flow of another flue gas having another sensible heat, the another flue gas initially flowing in the combustion chamber counter-currently with the first mixed-feed. In yet another variant, the apparatus includes at least another burner disposed in the combustion chamber. The another burner is adapted to combustor a portion of the fuel or another fuel, thereby generating a flow of another flue gas having another sensible heat, the another flue gas initially flowing in the combustion chamber in an initial direction other than co-currently or counter-currently with the first mixed-feed.
A second embodiment of the apparatus is similar to the first embodiment but includes a mixing means in the reaction chamber adapted for mixing the first mixed-feed and the second mixed-feed.
A third embodiment of the apparatus is similar to the first embodiment but includes a means for removing a product stream from the inner tubular portion of the tube-in-tube, the product stream flowing through the inner tubular portion counter-currently with the second mixed-feed.
A fourth embodiment of the apparatus includes: a combustion chamber, a convection chamber is fluid communication with the combustion chamber, at least two reaction chambers spaced apart in substantially parallel relationship, and a plurality of burners disposed in the combustion chamber. The combustion chamber has a first end and a second end opposite the first end. The convection chamber has a first end and a second end opposite the first end, the first end of the convection chamber being adjacent the second end of the combustion chamber. Each reaction chamber has a first part and a second part in fluid communication with the first part. A substantial portion of the first part is disposed in the combustion chamber and a substantial portion of the second part is disposed in the convection chamber. The second part is a tube-in-tube having an annular portion between an inner tubular portion and an outer tubular portion surrounding the inner tubular portion. Each burner is adapted to combustor a fuel, thereby generating a flow of a flue gas from the combustion chamber to the convection chamber, the flue gas having a sensible heat. At least one burner is positioned between the two reaction chambers, a first reaction chamber is positioned between the first burner and a second burner, and a second reaction chamber is positioned between the first burner and a third burner. The apparatus also has a means for flowing a first mixed-feed through the first part of each reaction chamber co-currently with the flow of the flue gas in the combustion chamber, and a means for flowing a second mixed-feed through the annular portion of the second part of each reaction chamber counter-currently with the flow of the flue gas in the convection chamber. In addition, the apparatus has a mixing means in each reaction chamber adapted for mixing the first mixed-feed and the second mixed-feed, and a means for removing a product stream from the inner portion of the tube-in-tube, the product stream flowing through the inner tubular portion counter-currently with the second mixed-feed.
A fifth embodiment of the apparatus includes: a combustion chamber, a convection chamber in fluid communication with the combustion chamber, at least one reaction chamber, and a plurality of burners disposed in the combustion chamber. The combustion chamber has a first end and a second end opposite the first end. The convection chamber has a first end and a second end opposite the first end, the first end of the convection chamber being adjacent the second end of the combustion chamber. The reaction chamber has a first part and a second part in fluid communication with the first part. A substantial portion of the first part is disposed in the combustion chamber and a substantial portion of the second part is disposed in the convection chamber. The second part is a tube-in-tube having an annular portion between the inner tubular portion and an outer tubular portion surrounding the inner tubular portion. Each burner is adapted to combustor a fuel, thereby generating a flow of a flue gas from the combustion chamber to the convection chamber, the flue gas having a sensible heat. The reaction chamber is positioned between a first burner and a second burner. The apparatus also includes a means for flowing a first mixed-feed through the first part of the reaction chamber co-currently with the flow of the flue gas in the combustion chamber, and a means for flowing a second mixed-feed through the annular portion of the second part of the reaction chamber counter-currently with the flow of the flue gas in the convection chamber. In addition, the apparatus includes a mixing means in the reaction chamber adapted for mixing the first mixed-feed and the second mixed-feed, and a means for removing a product from the portion of the tube-in-tube, the product stream flowing through the inner tubular portion counter-currently with the second mixed-feed.
A first embodiment of the method for producing a product from a steam reforming process includes multiple steps. The first step is to provide a combustion chamber having a first end and a second end opposite the first end. The second step is to provide a convection chamber in fluid communication with the combustion chamber, the convection chamber having a first end and a second end opposite the first end, the first end of the convection chamber being adjacent the second end of the combustion chamber. The third step is to provide a reaction chamber having a first part and a second part in fluid communication with the first part, a substantial portion of the first part being disposed in the combustion chamber and a substantial portion of the second part being disposed in the convection chamber, wherein the second part is a tube-in-tube having an annular portion between the inner tubular portion and an outer tubular portion surrounding an inner tubular portion. The fourth step is to combustor a fuel in the combustion chamber, thereby generating a combustion heat and a flow of a flue gas from the combustion chamber to the convection chamber, the flue gas having a sensible heat. The fifth step is to feed a first mixed-feed to the first part of the reaction chamber, wherein at least a portion of the first mixed-feed absorbs at least a portion of the combustion heat. The sixth step is to feed a second mixed-feed to the annular portion of the second part of the reaction chamber, wherein the second mixed-feed flows counter-currently with the flow of the flue gas in the convection chamber, whereby at least a portion of the second mixed-feed absorbs at least a portion of the sensible heat.
There are several variations of the first embodiment of the method. In one variation, the substantial portion of the first part of the reaction chamber is substantially vertical in the combustion chamber and the substantial portion of the second part of the reaction chamber is substantially vertical in the convection chamber. In a second variation, the second mixed-feed flows co-currently with the flow of the flue gas in the combustion chamber. There are several variants of the second variation. One variant includes an additional step of injecting a gas having another sensible heat near the second end of the combustion chamber, the gas initially flowing in the combustion chamber counter-currently with the first mixed-feed. Another variant includes an additional step of combusting a portion of the fuel or another fuel near the second end of the combustion chamber, thereby generating another combustion heat and a flow of another flue gas having another sensible heat, wherein another flue gas initially flows in the combustion chamber counter-currently with the first mixed-feed. Yet another variant includes an additional step of combusting a portion of the fuel or another fuel in the combustion chamber, thereby generating another combustion heat and a flow of another flue gas having another sensible heat, wherein the another flue gas initially flows in the combustion chamber in an initial direction other than co-currently or counter-currently with the first mixed-feed.
A second embodiment of the method is similar to the fist embodiment but includes the further step of mixing the first mixed-feed and the second mixed-feed in the reaction chamber.
A third embodiment of the method is similar to the first embodiment but includes the further step of removing a product stream from the inner tubular portion of the tube-in-tube, the product stream flowing through the inner tubing portion counter-currently with the second mixed-feed.
A fourth embodiment of the method includes a plurality of steps. The first step is to provide a combustion chamber having a first end and a second end opposite the first end. The second step is to provide a convection chamber in fluid communication with the combustion chamber, the convection chamber having a first end and a second end opposite the first end, the first end of the convection chamber being adjacent the second end of the combustion chamber. The third step is to provide at least two reaction chambers spaced apart in substantially parallel relationship, each reaction chamber having a first part and a second part in fluid communication with the first part, a substantial portion of the first part being disposed in the combustion chamber and a substantial portion of the second part being disposed in the convection chamber, wherein the second part is a tube-in-tube having an annular portion between an inner tubular portion and an outer tubular portion surrounding the inner tubular portion. The fourth step is to provide a plurality of burners disposed in the combustion chamber, each burner adapted to combustor the fuel, wherein at least one first burner is positioned between the two reaction chambers, a first reaction chamber is positioned between the first burner and a second burner, and a second reaction chamber is positioned between the first burner and the third burner. The fifth step is to combustor a fuel in the burners, thereby generating a combustion heat and a flow of a flue gas from the combustion chamber to the convection chamber, the flue gas having a sensible heat. The sixth step is to feed a first mixed-feed to the first part of each reaction chamber, wherein the first mixed-feed flows co-currently with the flow of the flue gas in the combustion chamber, and at least a portion of the first mixed-feed absorbs at least a portion of the combustion heat. The seventh step is to feed a second mixed-feed to the annular portion of the second part of each reaction chamber, wherein the second mixed-feed flows counter-currently with the flow of the flue gas in the convection chamber, whereby at least a portion of the second mixed-feed absorbs at least a portion of the sensible heat. The eighth step is to mix the first mixed-feed and the second mixed-feed in each reaction chamber. The ninth step is to remove a product stream from the inner portion of the tube-in-tube, wherein the product stream flows through the inner tubular portion counter-currently with the second mixed-feed.
A fifth embodiment of the method includes multiple steps. The first step is to provide a combustion chamber having a first end and a second end opposite the first end. The second step is to provide a convection chamber in fluid communication with the combustion chamber, the convection chamber having a first end and a second end opposite the first end, the first end of the convection chamber being adjacent the second end of the combustion chamber. The third step is to provide at least one reaction chamber having a first part and a second part in fluid communication with the first part, a substantial portion of the first part being disposed in the combustion chamber and a substantial portion of the second part being disposed in the convection chamber, wherein the second part is a tube-in-tube having an annular portion between an inner tubular portion and an outer tubular portion surrounding the inner tubular portion. The fourth step is to provide a plurality of burners disposed in the combustion chamber, each burner adapted to combustor a fuel, wherein the reaction chamber is positioned between a first burner and a second burner. The fifth step is to combustor a fuel in the burners, thereby generating a combustion heat and a flow of a flue gas from the combustion chamber to the convection chamber, the flue gas having a sensible heat. The sixth step is to feed a first mixed-feed to the first part of the reaction chamber, wherein the first mixed-feed flows co-currently with the flow of the flue gas in the combustion chamber, wherein at least a portion of the first mixed-feed absorbs at least a portion of the combustion heat. The seventh step is to feed a mixed-feed to the annular portion of the second part of the reaction chamber, wherein the second mixed-feed flows counter-currently with the flow of the flue gas in the convection chamber, whereby at least a portion of the mixed-feed absorbs at least a portion of the sensible heat. The eighth step is to mix the first mixed-feed and the second mixed-feed in the reaction chamber. The ninth step is to remove a product stream from the inner portion of the tube-in-tube, wherein the product flows through the inner tubular portion counter-currently with the second mixed-feed.